1. Field of the Invention
The present invention relates to an optical scanner, and more particularly, the present invention relates to a lase5r diode module which is a light emitting section for focusing on a photosensitive drum.
2. Description of the Related Art
An optical scanner which is generally applied to a laser printer, as shown in FIGS. 1 and 2, includes a housing 1 in which is disposed a light emitting section, that is, a laser diode module serving as a light source.
The laser diode module comprises a laser diode 3 for generating a laser beam, a collimator lens 4 for shaping laser beams emitted from the laser diode 3 into parallel beams, and a slitted member 5 formed with a rectangular hole 5a for passing therethrough only a portion of shaped parallel light beams.
Along paths of the beams passed through the slitted member 5, there are disposed a cylindrical leans 6 for converging the emitted beams into a sub scanning direction and a polygon mirror 7 having a plurality of reflecting faces for reflecting the beams passed through the cylindrical leans 6 at a predetermined angle of view while being rotated at a high speed.
Also, in front of the polygon mirror 7, there is positioned an f-.theta. lens, that is, a scanning lens 8 for spotting the beams onto a photosensitive drum 9. The canning lens 8 comprises a toric lens 8a and a focusing leans 8b which is an aspherical lens.
Hereafter, operations of the optical scanner constructed as mentioned above will be described in detail.
If a beam is emitted from the laser diode 3 constituting the laser diode module, the beam is converged into the sub scanning direction while passing through the rectangular hole 5a of the slitted member 5 and the cylindrical lens 6 after being shaped into parallel beams in a horizontal main scanning direction and the vertical sub scanning direction while passing through the collimator lens 4.
The beam converged into the vertical sub scanning direction as described above is reflected at the polygon mirror 7 rotating at a high speed such that it has a predetermined angle and then, is converged into the main scanning direction by the scanning lens 8 comprising the toric lens 8a and the focusing lens 8b, to be focused onto the photosensitive drum 9 thereby to realize a desired picture.
On the other hand, in the optical scanner, because, especially, the laser diode module is varied in assembling positions of respective lenses and conditions of focuses spotted onto the photosensitive drum 9, assembling operations must be performed with a high precision.
FIGS. 3 and 4 illustrate a conventional laser diode module is an assembled state.
The laser diode 3 is positioned on a board 10. A case 11 which is formed at its front part with an internally threaded portion 11a, is coupled to the board 10.
A holder 12 which is formed at its front part with an inserting groove 12a of a predetermined depth, is screwed into the internally threaded portion 11a of the case 11, and the collimator lens 4 is fitted into the inserting groove 12a of the older 12 by a fastener 13.
The slitted member 5 which is formed with the rectangular hole 5a, is coupled to a front portion of the holder 12.
At this time, a spring 14 is interposed between a front surface of the case 10 and a rear surface of the holder 12. The spring 14 functions to elastically bias the holder 12 outward to prevent the holder 12 from shaking by outside shock, etc.
In the laser diode module constructed as mentioned above, an optical axial distance adjustment operation of the collimator leans 4 is implemented by moving the holder 12 into which the collimator lens 4 is embedded, forward and backward along the case 11.
Further, as shown in FIGS. 3(a) through 3(c), an optical axis of the laser diode 3 is adjusted by moving the laser diode 3 which is fastened to the board 10 by fastening screws S leftward, rightward, upward and/or downward about the board 10 while screwing or unscrewing the fastening screws S.
However, the conventional laser diode module suffers from defects as described below.
First, since a multitude of components including the holder 12 into which the collimator lens 4 is embedded, the case 11, fastener 13 for fastening the collimator lens 4 to the holder 12, and the spring 14, are needed, the number of components is increased, whereby manufacturing cost is increased and assembling workability is deteriorated.
Second, because a tool for separately adjusting the holder 12 is needed so as to move the holder 12 forward or backward within the case 11, manufacturing cost is further increased.
Third, although the holder 12 is prevented to some extent from shaking by the spring 14 and the fastener 13, if outside shock continuously acts on the holder 12 or elastic force of the spring 14 is changed after a predetermined period of time the holder 12 is caused to move or shake, whereby the optical axial distance between the collimator lens 4 and the laser diode 3 varies.
Fourth, in the process of threading a circumferential inner surface of the case 11 and circumferential outer surface of the holder 12, a machining error maybe caused, whereby quality of end products cannot be uniformed.